In recent years, as electronic devices are becoming more sophisticated, there is a strong demand for semiconductor devices to be increasingly highly dense and integrated, and efforts are thus being made to make semiconductor devices (hereinafter also referred to as “semiconductor package” or “package”) to be higher in capacity and density. To satisfy such demands, for example, a lead on chip (LOC) structure in which a lead frame is adhered on a semiconductor element (hereinafter also referred to as “semiconductor chip” or “chip”) is employed. In the LOC structure, since a semiconductor element and a lead frame are combined, adhesion reliability at the joining area significantly affects the reliability of a semiconductor device.
In the past, an adhesive paste has been used to adhere a semiconductor element to a lead frame, but it was not always easy to apply the adhesive paste in an appropriate amount, and therefore there were cases in which the adhesive was squeezed out to the periphery of the semiconductor element.
To solve such a problem, for example, in the LOC structure, a film-type adhesive including an adhesive coated on a heat-resistant substrate, such as a hot melt-type adhesive film using a polyimide resin or the like, has been used (for example, refer to Patent Document 1). However, such a hot melt-type adhesive film needs to be applied under the high temperature, and therefore there were cases in which high density semiconductor elements and lead frames is thermal damaged.
In addition, in the recent semiconductor devices, there have been semiconductor devices that stack a semiconductor element on another semiconductor element in multiple layers, thereby making semiconductor devices smaller, thinner and larger in capacity. In such semiconductor devices, instead of the lead frame, the use of an organic substrate, such as a bismaleimide triazine substrate or a polyimide substrate, is increasing. With such an increase in organic substrates, it has become an important technical problem to avoid the occurrence of cracking caused by absorbed moisture inside the semiconductor device during the infrared reflow for soldering the semiconductor device, and it has been found that particularly the adhesive for semiconductor elements plays a very large role in such a technical problem.
The organic substrate used in semiconductor devices with a chip on chip (COC) structure in which a semiconductor element is stacked on another semiconductor element in multiple layers is not oriented for adhesion in a high temperature due to the inferior heat resistance compared with a lead frame. In addition, in a semiconductor device with a COC structure, the semiconductor element becomes thinner as the semiconductor device becomes thinner, and therefore thus far a problem occurs where the semiconductor element is significantly warped at a high adhesion temperature. From this, the demand is intensifying for a film-like adhesive capable of better than ever thermocompression bonding at a low temperature. As such a film-like adhesive, a hot melt-type adhesive film made of a mixture of a thermoplastic resin and a thermosetting resin has been suggested (for example, refer to Patent Reference No. 2 to No. 4).    Patent Reference No. 1: Japanese Laid-open Patent Application Publication No. H06-264035    Patent Reference No. 2: Japanese Laid-open Patent Publication No. 2002-121530    Patent Reference No. 3: Japanese Laid-open Patent Publication No. 2002-256235    Patent Reference No. 4: Japanese Laid-open Patent Publication No. 2003-096426